The present invention relates to the field of telephone switching equipment and, more particularly, to circuits for converting one telephone number to another telephone number.
Specific telephone services are typically requested by dialing a predetermined number. For example, "0" is used to reach the operator, 411 is typically used to reach an information operator. The central office digit receiver is programmed to recognize specific numbers and route then to the correct circuits.
Changes in the numbers used to request certain common services such as operator assistance are being forced by the need to accommodate several different telephone service companies. In addition new services which are extensions of previously offered services are being added. These changes either require the telephone subscriber to learn a new set of numbers for these common services, or they require that the central office switching circuitry be reprogrammed.
Where possible, the numbers which connect the subscriber to the new service in question should be extensions of the numbers used to connect the subscriber to the previous similar service. This minimizes the effort needed to remember the new numbers. For example, before the deregulation of the telephone industry, only one number was needed for operator assistance, i.e., "0". Since deregulation, each subscriber has a separate long distance service. Hence, the subscriber needs two different numbers for operator assistance, one for local operator assistance and one for long distance operator assistance. The most desirable choice for this second number, i.e., long distance operator assistance, would be "00". However, most existing switching circuitry recognizes "00" as requesting immediate connection to a local operator ("0" connects the subscriber to the local operator after a delay which is sufficient to determine if the "0" is followed by a telephone number). Hence to use "00" for long distance operator assistance, it would be necessary to reprogram the existing switching circuitry, which is a costly process.
It is important that any circuit for translating a subscriber dialed telephone number into a new number which is compatible with the existing central office switches not introduce delays into calls which do not require translation. For example, a simple translation circuit could be placed in series with the digit receiver of the central office between the subscriber and the digit receiver. In the simplest embodiment, such a circuit would receive the number dialed by the subscriber, check it against an internal list of numbers to be translated, and then outpulse the number or its appropriate translation to the digit receiver. However, it would have to repeat each number which is not to be translated. This would introduce a delay equal to the time needed to outpulse the entire telephone number into every telephone number dialed whether or not it required translation. This is unsatisfactory.
This delay can be significantly reduced by providing a means for recognizing numbers not requiring translation before the entire number is received. For example, the prefix of the number is sufficient in most cases to determine that it is not one of the numbers which needs to be translated. Such a system could then begin to outpulse the telephone number before it received the entire number from the subscriber. However, such a system would still need to receive at least the first digit of the number being dialed. Hence, even this system would introduce a delay equal to the time needed to repeat one digit into the system. Such delays increase the time needed to connect a call and hence increase the load on the switching system and digit receiver.
In addition to increasing the loads on the switching system, long delays in the translation of telephone numbers discriminate against suppliers of the new telephone services. Equal access to the telephone system for all suppliers of subscriber services requires that long delays not be introduced by the telephone switching system when supplying services by a company which is different from the one providing the local switching system. A long delay would make the outside service less attractive to the subscriber than a similar service provided by the company controlling the local switching system. Hence, a dialed number can not be satisfactorily translated into another number merely by placing a translating circuit in between the subscriber and the central office as described above.
It is a general object of the present invention to provide an improved circuit for converting one telephone number into another telephone number.
It is another object of the present invention to provide a means for converting a specified sequence of digits dialed by subscriber to a second predetermined series of digits without the need to reprogram the central office switching circuitry and without significantly increasing the average time required to connect a subscriber to a requested service.
It is a further object of the present invention to provide long distance operator service upon receiving the digit sequence "00".
These and other objects of the present invention will become apparent from the following detailed description of the invention and the accompanying drawings.